A Review of Corrosion Issues Related to Uranyl Nitrate Base Aqueous Homogeneous Reactors
Aqueous homogeneous reactors (AHRs) are liquid fuel nuclear reactors, typically consisting of an acidified nitrate or sulphate base solution of enriched uranium-235 (235U). The goal of this paper is to review both the report and research literature on the topic of materials corrosion issues related to uranyl nitrate base AHRs. The materials of interest are stainless steel (SS)347, SS304L, SS304L-NAG, SS316L and zirconium (Zr) base alloys. In nitric acid solutions, SS and Zr alloys are passive, although there is some increased susceptibility of SS347 to intergranular corrosion (IGC) and knife-line attack as compared to other alloys. This is likely a result of the higher carbon (C) content in SS347. In uranyl nitrate fuel simulants corrosion rates increased as compared with nitric acid alone with the corrosion rate of SS347 being the highest while SS316 was the lowest of the austenitic stainless steels tested. In comparison, corrosion rates of Zr based alloys remained relatively unchanged in uranyl nitrate base solutions. The most prominent issue for these materials appears to be iodide (I−) induced pitting corrosion on the walls of the off-gas extraction system with the potential for stress corrosion cracking. For Zr alloys, vapour phase I− pitting and SCC are well documented failure mechanisms with the threshold I− concentration being on the order of 1–2 ppm. In the off-gas extraction system of a 200 kW AHR calculations indicate that the I− concentration may be as high as 0·4–0·6 ppm warranting further study in this area. The influence of a prototypic AHR neutron flux on corrosion rates and susceptibility to underfilm corrosion, due to precipitation of UO2(OH)2, was not available from the literature.
Lillard, Robert, "A Review of Corrosion Issues Related to Uranyl Nitrate Base Aqueous Homogeneous Reactors" (2010). Chemical and Biomolecular Engineering Faculty Research. 434.